Suppose for a moment that the Queen of Lemuria whipped
up a pictographic writing system and bestowed it upon her
people, and that the Lemurian empire isn't mythical, and that
relics of that bygone age survived into modern times.

This pictographic writing system consisted of stylized forms
which were brightly multicolored by the happy-go-lucky
Lemurians (little did they know). Even though these people
enjoyed the colorful aspect of their writing, the symbols
themselves, stripped of their colors, were meaningful.

These citizens made up a new word for their writing system,
the notion that neologisms are symptomatic of psychopathology
notwithstanding. They called the individual characters in their
writing system "icons". Examples of the writing turn up from
time-to-time and are studied.

In modern times, there are 162 scholars world-wide studying
these Lemurian pictograms, although one of them is feeling
poorly. These scholars exchange data speculating about the
nuances of certain symbols. Some scholars make information
available on the web.

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Leaving mythical realms, would that sort of thing be encodable
as computer plain-text? I'd say yes. There's the universality
thing, the fact that it's a bona-fide writing system, and the
idea that black-and-white rendering doesn't alter the identity
or nature of the character. Of course, nobody would suggest
that any of the individual icons should be unified with
look-alike pre-existing characters scattered throughout the
standard, though, would they? After all, they're part of a set,
and nobody likes to break up a set.
Since establishing that emoji are (or are in the process of
becoming) a new style of pictographic writing would tend to lend
credibility to a proposal, we might presume that this is not the
case. Otherwise, emoji proponents would raise the issue and
provide supporting evidence, wouldn't they?
http://mobile.kaywa.com/default/emoji-and-emoticons-the-first-truly-universal-language.html
So, questions about whether these icons are being used more as
graphic embellishment (ornaments) to text, or are being used
in rebus are disregarded by emoji proponents, neither outcome
being likely to lend credibility to a plain-text proposal.
Instead, we are all asked to consider pragmatic interoperability
requirements. Opponents reply that, even granting such
requirements, the solution is beyond the realm of plain-text.
It is even inappropriate, opponents might say, to unify graphic
icons with their respective underlying textual symbols, if any.
After all, these emoji are part of a set. Many users exchanging
them probably expect to see exactly what they send wherever
they view them, no matter the application, no matter the platform.
So, the opponents say, let 'em use rich-text.
The proponents reply that it doesn't matter where your principles
stand, these icons must be encoded in the plain-text standard because
vendors in Japan are exchanging them via PUA characters hacking
plain-text protocols. The opponents say that the very fact that
it's a hack lends credence to the idea that these icons are not textual
in nature. The proponents remind us of pragmatic interoperability
and advise everybody to get over it. Proponents say that we must
have them in Unicode, opponents say why not just stick them up
in one of the higher PUA planes and be done with it.
Is that as dumb as it sounds? It's my understanding that Google
already handles some emoji using PUA characters. If Google has
code and charts, perhaps Google could undertake an ad-hoc PUA
registry along the lines of ConScript Unicode Registry, using
one of the higher PUA planes. This would keep the icons together
as a set and allow for future expansion. "Hacking" plain-text
protocols would continue, but nobody cares what you do in the PUA.
Unicode could place a note into the Standard explaining that such
and such PUA plane is generally regarded as a corporate private
use graphic symbol registry and be done with it. People who
want to see multicolored blobs transformed into black-and-white
ones in their text applications could do so, and people wanting
to see the actual multicolored icons could continue using higher
level protocols to do so.
How much actual interchange is being done using the PUA planes?
I don't have the resources to find out, but I'll bet it's mighty lean.
Of course, unscrupulous types might do things which conflict
with a high plane PUA, there's nothing stopping them. Just like
there's nothing stopping a designer making an 8-bit "hack" font
and putting logos and icons in slots reserved for ASCII.
With the dearth of any other higher plane PUA usage, an
application encountering such characters would have a fairly
good clue as to how to process/interpret the strings.
The PUA is a good place for a de-facto standard. Google has
an interest in interoperability and has already done much of
the work.
Best regards,
James Kass
P.S. - Much of the above was probably cobbled together from posts
by many people on more than one list. I don't claim authorship for
any of it unless there are royalties involved beyond the Queen of
Lemuria.